Semiconductor devices having a so-called MOS structure such as an IGBT (Insulated Gate Bipolar Transistor) and a MOSFET (MOS Field Effect Transistor) have been known. In such a MOS type semiconductor device, an overvoltage protection diode configured of Zener diodes connected in series is used as a protective measure against overvoltage. Specifically, the overvoltage protection diode is configured such that an N-type semiconductor layer and a P-type semiconductor layer are alternately arranged adjacently to each other. In the case of an IGBT, an overvoltage protection diode is provided between a collector terminal and a gate terminal or between a gate terminal and an emitter terminal.
In a conventional semiconductor device 100, the top surface of a semiconductor substrate 120 includes an active region A on which main electric current flows, and a voltage supporting region B surrounding the active region A. Further, as illustrated in FIG. 14, an overvoltage protection diode 150 is provided so as to protrude from a side portion to the center portion of the semiconductor substrate 120. Furthermore, the periphery of the semiconductor substrate 120 is provided with conductors (field plates) 160, 170, 180, and 190 made of a conductive material, in order to make the surface potential of the voltage supporting region stable. To allow the conductors 160, 170, 180, and 190 to connect to predetermined portions of the overvoltage protection diode 150, a connection region Bc exists as illustrated in FIG. 14.